System exceptions and Application exceptions

Hi
  There are 2 important classes in the hierarchy that are derived from System.Exception:
1)System.SystemException:-
               This class is for exceptions that r usually thrown by the .net runtime, or which r considered to be of a generic nature and must be thrown by almost any application. For example, StackOverflowException will be thrown by the .net runtime if it detects the stack is full. On the other hand, u might choose to throw ArgumentException or it's subclasses in ur code, if u detect that a method has been called with inappropriate arguments. Subclasses of System.SystemException includes classes that represent both fatal and non-fatal errors.
2)System.ApplicationException:-
             This class is important, becoz it is the intended base for any class of exception defined by third parties. Hence, if u define any exceptions covering error conditions unique to ur application, u should derive these directly or indirectly from System.ApplicationException

For more detail you can refer below links:-
http://www.merithub.com/q/113-difference-system-exceptions-application-exceptions.aspx
http://www.interviewqsn.com/difference-between-system-exception-and-application-exceptions.html